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Miralles I.,EEZA | Trasar-Cepeda C.,CSIC - National Institute of Agrobiological Sciences | Leiros M.C.,University of Santiago de Compostela | Gil-Sotres F.,University of Santiago de Compostela
Soil Biology and Biochemistry | Year: 2013

Decomposition processes are extremely important in biological soil crusts (BSCs). Although the effects of temperature and moisture on such processes have been widely studied, little is known about the influence of the readily metabolizable substrate (labile C) and how this substrate varies in different types of BSCs. In the present study, BSCs formed by cyanobacteria (CYANO) and by lichens (DIPLOS and LEPRA) were incubated at 25 °C (optimum temperature) and different moisture levels, for evaluation of the pool of labile C in the crust layers. Labile C was estimated as the sum of CO2-C emitted and the C extracted with hot water (80 °C) at the end of the incubation period. In all crusts, the relationship between emission and moisture fitted a quadratic model. For the different moisture contents, the sum of CO2-C emitted and C extracted with hot water converged to a constant value for each type of crust. This value, considered as the maximum content of labile C in the crust, was extremely high in DIPLOS, reaching up to 40% of the total organic C (TOC) initially present. In all crusts, and independently of the consumption of labile C, simple sugars (sucrose, glucose) remained at the end of the incubation period, which suggests that these sugars may play a protective role in BSCs. The presence of mannitol suggests that the fructose released during hydrolysis of sucrose was reduced to mannitol, thus enabling electron transport during moments of intense respiratory stress. The intense respiration in DIPLOS is partly due to the metabolism of polyphenols, which are possibly derived from the growth and death of free-living fungi that proliferate during incubation of the crusts. These results demonstrate that the metabolic processes in BSCs differ depending on the type of organisms that form the crusts and that there is a high risk of C loss from Diploschistes BSCs after heavy rainfall events. © 2012 Elsevier Ltd. Source

Guntinas M.E.,University of Santiago de Compostela | Leiros M.C.,University of Santiago de Compostela | Trasar-Cepeda C.,CSIC - National Institute of Agrobiological Sciences | Gil-Sotres F.,University of Santiago de Compostela
European Journal of Soil Biology | Year: 2012

Climate change will lead to changes in soil moisture and temperature, thereby affecting organic matter mineralization and the cycling of biophilic elements such as nitrogen. However, very few studies have considered how the sensitivity of the rate of net nitrogen mineralization to temperature and/or moisture content may be modified by changes in these parameters. To investigate how changes in temperature and moisture content affect net nitrogen mineralization (as regards both the mineralization rate and the sensitivity of the mineralization rate to changes in temperature and moisture content), a laboratory experiment was carried out in which three soils under different types of use (Forest, Grassland, Cropland) were incubated for 42 days under different moisture conditions (between 40 and 100% field capacity) and temperatures (between 10 and 35 °C); total inorganic nitrogen levels were determined at different times throughout the experiment. The rate of mineralization was determined at each temperature and moisture level considered, by use of the mono-compartmental model developed by Stanford and Smith (1972). For all soils, changes in the rate of mineralization with temperature followed the pattern described by the Q 10 model, while the models used to determine the effect of moisture content on the net rate of mineralization (linear, semilogarithmic, partial parabolic and complete parabolic) were only verified for the Forest soil. In general, the sensitivity to temperature was maximal at 25 °C, and the optimal moisture content for nitrogen mineralization was between 80% and 100% of field capacity. A relatively simple model that included the temperature-moisture-time interaction was also tested. This model provided a significant fit for the three soils under study, in contrast with the other models tested. In any case, further studies are necessary in order to address the extent to which changes in the quality of organic matter, caused by land use, affect any modifications to soil nitrogen that may be generated by climate change. © 2011 Elsevier Masson SAS. Source

Couto-Vazquez A.,CSIC - National Institute of Agrobiological Sciences | Gonzalez-Prieto S.J.,CSIC - National Institute of Agrobiological Sciences
Trees - Structure and Function | Year: 2010

Needles, annual rings from basal stem discs and bark of three dominant and three suppressed Pinus pinaster from a 12-year-old pine stand (naturally regenerated after a wildfire) were analysed to study the effects of climate, tree age, dominance, and growth on tree δ15N. Foliar-N concentration in dominant pines (0.780-1.474% N) suggested that soil N availability was sufficient, a circumstance that allowed isotopic discrimination by plants and (greater) differences in δ15N among trees. The δ15N decreases in the order wood (-0.20 to +6.12‰), bark (-1.84 to +1.85‰) and needles (-2.13 to +0.77‰). In all trees, before dominance establishment (years 1-8), the N stored in each ring displayed a decreasing δ15N tendency as the tree grows, which is mainly due to a more "closed" N cycle or an increasing importance of N sources with lower δ15N. After dominance establishment (years 9-12), wood δ15N values were higher in suppressed than in dominant trees (2.62 and 1.46‰, respectively; P < 0.01) while the reverse was true for needles and bark; simultaneously, the absolute amount of N stored by suppressed pines in successive rings decreased, suggesting a lower soil N assimilation. These results could be explained by lignification acting as major N source for needles in suppressed pines because products released and reallocated during lignification are 15N-depleted compared with the source. According to principal component analysis, wood δ15N appears associated with wood N concentration and precipitation during the growing season, but clearly opposed to age, basal area increment and mean temperature in spring and summer. © 2010 Springer-Verlag. Source

Gomez-Rey M.X.,CSIC - National Institute of Agrobiological Sciences | Gonzalez-Prieto S.J.,CSIC - National Institute of Agrobiological Sciences
Biology and Fertility of Soils | Year: 2013

Wildfires often modify soil properties, including the N status and net N mineralization rates, but their impacts on gross N fluxes have been scarcely evaluated. We aimed to ascertain the immediate effects of a medium-high severity wildfire on soil N transformations. Net and gross N rates were analytically and numerically (FLUAZ) quantified in burned (BS) and unburned (US) topsoils from the temperate-humid region (NW Spain). Analytical and numerical solutions were significantly correlated for both gross N mineralization (m) (r 2 = 0.815; p < 0.001) and gross nitrification (n) (r 2 = 0.950; p < 0.001). In BS, all NH4 +-N fluxes (net m, gross m and gross NH4 +-N immobilization, 'ia') increased, while those of NO3 --N decreased (gross n and gross NO3 --N immobilization, 'in') or did not vary (net n). In US and BS, gross m (0.26-3.60 and 4.70-15.42 mg N kg-1 day-1, respectively) predominated over gross n (0.026-2.45 and 0.001-0.002 mg N kg-1 day-1, respectively), and the same was true for the net fluxes. Compared with the few available data on recently burned soils (m = 8-55 mg N kg-1 day-1; n = 0.50-1.83 mg N kg-1 day-1), our gross m and n rates were similar and very low, respectively; gross n showed that nitrifiers were active in US and also in BS, despite the 98 % reduction observed immediately after the fire. For gross fluxes, m increased more than ia suggesting an NH4 +-N accumulation, but there is no risk of NO3 --N leaching because n decreased more than in. © 2013 Springer-Verlag Berlin Heidelberg. Source

Gomez-Rey M.X.,CSIC - National Institute of Agrobiological Sciences | Gonzalez-Prieto S.J.,CSIC - National Institute of Agrobiological Sciences
Science of the Total Environment | Year: 2014

In NW Spain, a European region with very high fire incidence and erosion risks, the effects on soils of a medium-to-high severity wildfire and two emergency stabilization techniques were studied. In burned plots (control, BS; seeded with cereal, BSS; straw mulched, BSM) and adjacent unburned plots (US), the topsoil (0-2cm) pH and thirteen NH4Ac-DTPA extractable elements were evaluated at t=0, 4, 8 and 12months after the fire. Compared to US, fire increased by 0.3-0.5units the soil pH which decrease slowly over time, but remaining significantly higher at t=12 (BS, BSM, BSS>US). Ammonium nitrogen (N) levels were higher (p<0.05) in burned plots than in US, difference decreasing progressively from 48-fold (t=0) to 25-fold (t=12). Although no significant effect of fire was immediately observed, the extractable sodium (Na) and potassium (K) were higher (p<0.05) in burned plots than in US at t=4 and t=8, probably due to cation leaching from the overlying ash. Fire did not modify the extractable magnesium (Mg), but at t=0 the extractable calcium (Ca) and phosphorous (P) were transiently and significantly higher in burned plots than in US. Extractable aluminum (Al), iron (Fe), copper (Cu), cobalt (Co) and zinc (Zn) were lower and manganese (Mn) was higher in burned plots than in US. Neither seeding nor mulching significantly modified the topsoil concentrations of the elements considered. The PCA revealed that BS, BSM and BSS became more similar to US over the study period due to a rapid decrease in extractable Ca and Mg and a slow decrease in extractable Mn and NH4 +-N. At t=12, the most notable differences between burned plots and US were in the concentrations of extractable Al and Zn. Data suggest that at least another 4-8months will be required for full recovery of the burned plots to unburned conditions. © 2014 Elsevier B.V. Source

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